A currently popular water heater display panel displays temperature by a LED digital tube on the market. Operation condition of the water heater is indicated by different colors of LED indicator, and water temperature modes are selected with a key switch. However, actual application does not require very precise temperature value. Control circuit is complex by the LED digital tube to display temperature, and cost of the water heater is also increased. Water temperature modes have disadvantages by the key switch way to select control, because operation environment of the water heater is kitchen with relatively humid environment. The key switch is easy to get damp after using in such bad environment for a period of time. As a result, final hot water out of the water heater does comply with set water temperature mode, and the water heater out of control also will continuously heat and lead to constant waste of energy.